FIG. 1 illustrates a schematic diagram of a prior art status indicator utilized on the L1011 aircraft for providing a visual indication of the coupling status of the connection between rotary power applied from an aircraft propulsion engine (not illustrated) to input shaft 14 of an integrated drive generator (IDG) 16 of conventional construction. A more complete explanation of the status indicator is contained in pages 1-17 of the Sundstrand Aviation 90IDG01 Maintenance Manual. An IDG is an integral unit having a constant speed drive transmission which converts variable velocity rotary power inputted by shaft from an aircraft propulsion engine into a constant speed shaft drive which drives a power generator for producing constant frequency three phase 400 Hz electrical power. A constant speed drive (CSD) performs the same function as an IDG but is not an integral unit. The IDG 16 contains an internal coupling mechanism 20 which receives rotary power from shaft 14 and couples rotary power by a shaft connection 21 to a conventional constant speed drive transmission 22 when the coupling mechanism is in a first position. In response to a control signal the coupling mechanism 20 decouples rotary power applied to the input shaft 14 from the constant speed drive (CSD) transmission 22. The transmission 22 has a constant speed output shaft 21' connected to a 3.phi. power generator 23 when the control signal is not present. The CSD transmission 22 converts the variable velocity shaft input coupled thereto by the shaft coupling 21 into a constant velocity output on coupling 21' which drives the electrical generator 23 to produce constant frequency multiple phase electrical power. A magnetic status indicator 24 is contained within the coupling mechanism 20 which provides a visual indication of the status of the connection of the shaft 14 to shaft 21 of the coupling mechanism 20 to ground personnel by opening of the cowling associated with the propulsion engine. The magnetic status indicator relies upon magnetic attraction of two magnets with one of the magnets being connected to a movable part within the coupling mechanism 20 such that when the coupling mechanism is connected, the status indicator button 26 is in a first position and when the coupling mechanism is disconnected, the status indicator button is in the second position.
The magnetic status indicator 24 has not proven in service to be totally reliable in indicating the status of the connection of the input shaft 14 to the CSD transmission 22. Vibration has caused the part in the coupling mechanism 20 on which one of the magnets is mounted to move sufficiently to lose magnetic attraction with the other magnet to cause the button 26 to move to the position indicating disconnection to give a false indication that the coupling mechanism 20 is disconnected. Furthermore, a landing involving high inertial forces has caused the part on which one of the magnets is mounted within the coupling mechanism 20 to move to lose magnetic attraction to cause the button 26 to move to the position indicating disconnection to provide a false indication. A false indication by the button 26 of the magnetic status indicator 24 causes ground personnel to search for a problem within the IDG 16 requiring further inspection to verify that the IDG is operational. The time required for the inspection may delay the aircraft from meeting departure schedules.